The present invention relates to an image forming apparatus such as a full color copying machine or a color printer.
A so-called 4-series-tandem type full color copying machine has been conventionally known as an image forming apparatus which outputs a color image. In a four-tandem full color copying machine, four image forming units which respectively form yellow (Y), magenta (M), cyan (C) and black (BK) toner images on the basis of a color-separated image signal are disposed along a conveying belt.
Each color image forming unit includes a photo-sensitive drum which rotatably contacts a conveying belt, a charging device which charges a drum surface to a predetermined potential, an exposure device which exposes the drum surface with light to form an electrostatic latent image, a development device which supplies toner to the electrostatic latent image on the drum surface to develop the electrostatic latent image, and a transfer device which transfers the developed toner image to a recording sheet which is being adsorbed and conveyed on the conveying belt. In this way, the recording sheet adsorbed on the conveying belt is conveyed through four image forming units (process units). Color toner images are transferred to the recording sheet in a superposed manner, and the recording sheet is fed to a fixing device. At the fixing device, the color toner images are fixed onto the recording sheet so as to form a color image.
The above-described four-tandem color copying machine is configured by a scanner section, an image processing section, an image compression section, an image register section (HDD), an image expansion section and a printer section.
Recently, in accordance with an increase in the capacity of the image register section (HDD), at the time of performing color copy, a scanned image is compressed and then stored in an HDD or the like. The compressed image is read out and re-formed. Then, the re-formed image is printed.
If the compression is performed with a low compression rate (high image quality), the amount of compressable image data is increased. As the result, the copy speed becomes low. If the compression is performed with a high compression rate, the image quality is deteriorated, but the copy speed is increased.
When a user designates the compression rate (in operation, the user designates “high image quality”, “normal” or the like) and then scanning is performed, a sufficient image quality may be maintained by the compression rate or may not be maintained by the compression rate. In order to solve the problem, a pre-scanning is performed so as to automatically set an optimized compression rate. However, there may be a case in which a user does not need a high image quality (low compression rate). Therefore, a user's demand cannot be reflected precisely.